1. Field of the Invention
The present invention relates to a sheet registering device for registering a plurality of sheets, supplied to a tray, longitudinally and transversely and, more particularly, to a sheet registering device to be applied to a finish-processing device for transporting the sheets while arranging the postures of the sheets and their positional relations to a reference position.
2. Description of the Related Art
In the prior art, some image forming apparatus such as a copying machine for copying the image of an original on a sheet of paper is equipped, as disclosed in Japanese Unexamined Patent Publication JP-A 1-104563, with a sheet finish-processing device for stapling a plurality of sheets. In this sheet finish-processing device, a paddler (having elastic blades) is arranged at an oblique position with respect to a sheet transporting direction, so as to register the sheets supplied to a tray with respect to a reference position. The sheet finish-processing device is further equipped with a mechanism for shifting the paddler to a position which is out of contact with a bundle of the finish-processed (or stapled) sheets, so as to avoid any obstruction to the discharge of the sheet bundle.
With the construction described above, however, the shift of the paddler to the position out of contact with a sheet bundle each time of discharging the sheet bundle will cause a loss in the time when a plurality of sheet bundles are to be made. This is so because the supply of the sheets from the image forming apparatus to the tray has to wait until the paddler returns to the reference position where it can register the sheets.
Unless the paddler is shifted to the position out of contact with the sheet bundle so as to raise the efficiency for preparing the sheet bundle, the sheets cannot be registered. This is because the position where the rotation of the paddler is stopped is not fixed. Specifically, if the sheets are registered widthwise (or transversely) by widthwise registration means, the sheet, as stacked at the uppermost position, is depressed downward by the paddler so that the frictional force of the paddler on the sheets exceeds that between the sheets.
If the registering force of the widthwise registration means is raised, moreover, the sheets are subjected, while being depressed by the paddler, to a transverse force by the widthwise registration means and may possibly be folded or broken.